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                <a class="post-title-link" href="/posts/cbce658b.html" itemprop="url">面试官：你是如何判断一个线程池需要创建多少个线程</a></h1>
        

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          <p>目前按照我看过的一些开源框架，线程池中线程数量主要是根据应用的类型：IO密集型（2n +1 ），CPU密集型设置为 n + 1。</p>
<p>但实际情况往往复杂的多，不会按照这个进行设置，进行这种设置，通常是框架层面，例如netty,dubbo这种底层通讯框架会参考这样的标准去设置，在实际业务中往往不会这样做。</p>
<p>对于IO密集型网上还有一个公式：线程数 = CPU核心数/(1-阻塞系数)</p>
<p>这个阻塞系数一般为0.8~0.9之间，可以取0.8或者0.9。</p>
<p>我觉这个公式有一定的道理，考虑了阻塞的概念。</p>
<p>在我们的业务开发中，基本上都是IO密集型，因为往往都会去操作数据库，访问redis，es等存储型组件，涉及磁盘IO，网络IO。</p>
<p>那什么场景下是CPU密集型呢？纯计算类，例如计算圆周率的位数，当然我们基本接触不到。</p>
<p><strong>IO密集型，可以考虑多设置一些线程，主要目的是可以增加IO的并发度，CPU密集型不宜设置过多线程，因为是会造成线程切换，浪费时间。</strong></p>
<p><strong>接下来我们以一个实际的场景来说明如何设置线程数量。</strong></p>
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          <p>Redis不需要Leader这个观点其实有歧义，是不准确的，题目的问题本质其实是涉及数据分片、数据复制一致性。</p>
<h2 id="1、Redis-Cluster-架构"><a href="#1、Redis-Cluster-架构" class="headerlink" title="1、Redis Cluster 架构"></a>1、Redis Cluster 架构</h2><p>在Redis3.0版本开始，Redis引入了一种去中心化的集群架构，采用预分片的模式，一个集群中所有节点总共对应16384个槽位，在对一个key进行写入时，首先对key取hashcode，然后求模来映射到具体的某一个节点，其部署架构如下图所示：<br><img src="https://img-blog.csdnimg.cn/20210322115450433.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ByZXN0aWdlZGluZw==,size_16,color_FFFFFF,t_70#pic_center" alt="在这里插入图片描述"><br>上述每一个节点中存储的数据都不一样，即每一个节点存储整体数据的一部分，<strong>并且为了实现去中心化</strong>每一个节点需要存储集群中所有key所对应存档的节点信息(即Key的路由信息)，这样当客户端将查询key1的请求发送到redisA节点，但该key1实际存储在redisB节点，此时A节点需将该节点路由到实际存储该key的节点，内部实现一个重定向，从而实现访问任意一个节点都能查询到存储的值。</p>
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          <h2 id="１、面试场景与面试技巧"><a href="#１、面试场景与面试技巧" class="headerlink" title="１、面试场景与面试技巧"></a>１、面试场景与面试技巧</h2><p>金三银四招聘季，一位粉丝朋友最近在蚂蚁金服第二轮面试时遇到这样一个问题：<strong>如果MQ消费遇到瓶颈时该如何处理</strong>?。</p>
<p><strong>横向扩容</strong>，相比很多读者与我这位朋友一样会脱口而出，<strong>面试官显然不会满意这样的回答</strong>，然后追问道：<strong>横向扩容是堆机器，还有没有其他办法呢</strong>？</p>
<p>在面试过程中，个人建议大家在听到问题后稍作思考，不要立马给出太直接的答案，而是应该与面试官进行探讨，一方面可更深刻的理解面试官的出题初衷，同时可以给自己梳理一下思路。</p>
<p>消费端遇到瓶颈，<strong>这是一个结果，但引起这个结果的原因是什么呢？</strong>在没有弄清楚原因之前<strong>谈优化、解决方案都会显得很苍白</strong>。</p>
<p>在这样的面试场景中，我们该如何探讨交流呢？我的思路如下：</p>
<ul>
<li>尝试与面试官探讨如何判断消费端遇到瓶颈</li>
<li>如何查找根因 </li>
<li>提出解决方案</li>
</ul>
<blockquote>
<p>温馨提示：为了本文观点的严谨性，本文主要以RocketMQ为例进行剖析。</p>
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          <h2 id="1、活动中心场景介绍"><a href="#1、活动中心场景介绍" class="headerlink" title="1、活动中心场景介绍"></a>1、活动中心场景介绍</h2><p>在电商系统上线初期，往往会进行一些“拉新”活动，例如活动部门提出<strong>新用户注册送积分、送优惠券活动</strong>。</p>
<p>基于分布式、微服务的设计理念，通常的架构设计（子系统交互）如下图所示：<br><img src="https://img-blog.csdnimg.cn/20210306232931379.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ByZXN0aWdlZGluZw==,size_16,color_FFFFFF,t_70#pic_center" alt="在这里插入图片描述"><br>其核心系统介绍如下：</p>
<ul>
<li>账户中心<br>提供用户登录、用户注册等服务，一个新用户注册时，向MQ服务器中的USER_REGISTER主题发送一条消息，主流程结束，与送积分，送优惠券等过程解耦。</li>
<li>优惠券（券系统）<br>提供发放优惠券、使用优惠券等与券相关的基础服务。</li>
<li>积分中心<br>提供积分相关的服务，例如积分赠送、积分消费、积分查询等基础服务。</li>
<li>送积分服务（消费者）<br>订阅MQ，按照规则决定是否需要赠送积分，如果需要则调用积分相关的基础接口，完成积分的发放。</li>
<li>送优惠券（消费者）<br>订阅MQ，按照规则决定是否需要赠送优惠券，如果需要则调用券系统相关的基础接口，完成优惠券的发放。</li>
</ul>
<p>上面的架构设计非常优雅，但并不是无懈可击，读者们肯定会想到<strong>如果新用户注册成功，但消息发送到MQ失败，或者消息成功发送到MQ，但发送完MQ后系统出现异常导致用户注册失败又该如何呢？</strong></p>
<p>上面的问题其实就是<strong>典型的分布式事务问题</strong>：即如何保证<strong>用户注册(数据库操作)与MQ消息发送</strong>这两个分布式操作的一致性。</p>
<p><strong>RocketMQ事务消息闪亮登场</strong>。</p>
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          <p>Netty是一款非常优秀的网络编程框架，是对NIO的二次封装，本文将重点剖析Netty服务端的启动流程，深入底层了解如何使用NIO编程服务端。</p>
<p><strong>本文是笔者基于问题的启发式源码阅读技巧的展示</strong>，建议带着如下问题开始本文的阅读：</p>
<ul>
<li>ServerBootstrap 的 option 与 childOption 分别有什么作用</li>
<li>服务端IO通道如何绑定事件链。</li>
<li>ServerBootstrap 的 handler 方法与 childHandler 方法的区别又是什么？</li>
<li>childHandler中的方法在服务端bind方法时会被调用吗？</li>
</ul>
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          <p>面试中一致性哈希算法被问到的概率非常大，本文将从如下三个方面探探一致性哈希算法，让大家轻松应对面试，并且说出宇宙不同的答案。</p>
<ul>
<li>一致性哈希算法经典实用场景</li>
<li>一致性哈希算法通常不适合用于服务类负载均衡</li>
<li>面试应对之策</li>
</ul>
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          <p>Netty是一款非常优秀的网络编程框架，是对NIO的二次封装，本文将重点剖析Netty客户端的启动流程，深入底层了解如何使用NIO编程客户端。</p>
<p>本文是笔者<strong>基于问题的启发式源码阅读技巧的展示</strong>，请带着如下问题开始本文的阅读：</p>
<ul>
<li>Netty是如何将客户端的事件加入到事件链中？</li>
<li>Netty客户端在启动时需要注册读事件？</li>
<li>Netty客户端在启动时需要注册写事件？</li>
<li>如果让你基于NIO写一个客户端需要实现的关键点是什么呢？</li>
</ul>
<p><strong>上面的问题也可以这样问：在使用NIO实现客户端时该注册哪些事件？</strong></p>
<p>本节将详细学习Netty4客户端的启动流程，我们从一个Netty客户端使用示例入手。</p>
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          <p>Dubbo在众多的微服务框架中脱颖而出，占据RPC服务框架的半壁江山，非常具有普适性，熟练掌握 Dubbo的应用技巧后深刻理解其内部实现原理，让大家能更好的掌控工作，助力职场，特别能让大家在面试中脱颖而出。</p>
<p>那Dubbo内部的设计理念，实现原理是什么呢？</p>
<p>本文将结合官方提供的3张图，从如下三个方面介绍其内部的核心实现、以及如何指导实践。</p>
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                <a class="post-title-link" href="/posts/4ec081f3.html" itemprop="url">面试官:Netty的线程模型可不是Reactor这么简单</a></h1>
        

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          <p>笔者看来Netty的内核主要包括如下图三个部分：<br><img src="https://img-blog.csdnimg.cn/20210109203705225.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ByZXN0aWdlZGluZw==,size_16,color_FFFFFF,t_70#pic_center" alt="在这里插入图片描述"><br>其各个核心模块主要的职责如下：</p>
<ul>
<li><p>内存管理<br>主要提高高效的内存管理，包含内存分配，内存回收。</p>
</li>
<li><p>网通通道<br>复制网络通信，例如实现对NIO、OIO等底层JAVA API 的封装，简化网络编程模型。</p>
</li>
<li><p>线程模型</p>
<p>提供高效的线程协作模型。</p>
</li>
</ul>
<p>大家不妨回想一下在以往的面试的过程中，面试官通常会问：<strong>Netty 的线程模型是什么？</strong></p>
<p><strong>主从多 Reactor 模型</strong>，相信大家都能脱口而出，然后呢？就没有然后了？</p>
<p>线程模型在网络通信中主要解决什么样的问题？在 Netty 中又是如何解决的，Netty 的线程模型为什么如此高效？请容我慢慢道来。</p>
<blockquote>
<p>温馨提示：为了保证文章观点的严谨性，将探究领域锁定在：Netty NIO 相关。</p>
</blockquote>
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                <a class="post-title-link" href="/posts/ff6cd24b.html" itemprop="url">一文揭晓通信协议设计的奥妙，直接“秒杀“面试官</a></h1>
        

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          <p>上一篇详细介绍了Netty的编解码的基本实现原理，本节将重点探讨网络编程中一种非常通用的协议设计方法论：<strong>协议头 + 消息体</strong>。</p>
<p>所谓的通信协议就是通信双方共同遵循的一种“约定”，用于通信发送方将内容按照“通信协议”所规定的格式组装成<strong>“二进制流”</strong>，通信接收方按照“通信协议”所规定的格式正确的从二进制流中解码出一个个原始请求。</p>
<p><strong>那通信协议如何设计呢？</strong></p>
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